Endocrine System

Question 1

Overview

Answer 1

• Includes ductless glands and endocrine tissues within other organs
• Secrete chemical signals called hormones which travel in the circulation and bind to receptors on/within target cells to initiate a change in the cell (a response)
  
  • Target Cell = cell with receptor specific for that hormone
  • No Target Cell = don’t have a receptor for hormone

Question 2

What are the 3 Hormone Classes?

Answer 2

1. Steroids
2. Hormones derived from amino acids
3. Peptide and protein hormones

Question 3

Steroids

Answer 3

• Synthesized (made) from cholesterol
• Testosterone, estrogen, vitamon D

Question 4

Hormones derived from amino acids

Answer 4

• e.g formed from tyrosine
  
  • Thyroxine/T4
    - A thyroid hormone
    - Controls cellular metabolism, growth and development
  • Epinephrine and norepinephrine (adrenaline and noradrenaline)
    - Secreated by the adrenal medulla as part of the fight or flight stress response and sexual climax (orgasm)

Question 5

Peptide and protein hormones

Answer 5

• Chains of amino acids held together by peptide bonds
• E.g. oxytocin, antidiuretic hormone (ADH), growth hormone (GH), insulin

Question 6

Endocrine Glands

Answer 6

Glands with no other function (pure endocrine glands - their only function is to produce and secrete hormones)

Question 7

How many Endocrine Glands?

Answer 7

1. Pituitary Gland
2. Thyroid Gland
3. Parathyroid Glands
4. Adrenal Glands

Question 8

Pituitary Gland

Answer 8

• Suspended from hypothalamus
• In sella turcica of sphenoid bone
• 2 lobes:
  
  1. Anterior Pituitary
  2. Posterior Pituitary

Question 9

Anterior Pituitary

Answer 9

• Glandular epithelial tissue
• Anterior pituitary hormone secretion regulated by hormones released by hypothalamus
• Secretes the following hormones:
  
  1. Growth Hormone (GH)
  2. Thyroid Stimulating Hormone (TSH)
  3. Adrenocorticotropic Hormone (ACTH)
  4. Gonadotropins - Reproductive Hormones
  5. Prolactin (PRL)

Question 10

Growth Hormone (GH)

Answer 10

Affects growth and metabolism

Question 11

Thyroid Stimulating Hormone (TSH)

Answer 11

Stimulates secretions by the thyroid gland

Question 12

Adrenocorticotropic Hormone (ACTH)

Answer 12

Stimulates secretion of steroid hormones from the adrenal gland

Question 13

Gonadotropins - Reproductive Hormones

Answer 13

• Luteinizing Hormone (LH)
  
  • Stimulates ovulation and formation of corpus luteum in the ovary; stimulates testosterone production by interstitial endocrine (Leydig) cells in the testes
• Follicle Stimulating Hormone (FSH)
  
  • Stimulates sustentocytes and follicle cells

Question 14

Prolactin (PRL)

Answer 14

Stimulates milk production by mammary glands

Question 15

Posterior Pituitary

Answer 15

• Nervous tissue (extension of brain structure called the hypothalamus)
• Stores and secretes hormones produced in hypothalamus, including:
  
  • Oxytocin
  • Antidiuretic Hormone (ADH, also known as vasopressin)

Question 16

Oxytocin

Answer 16

Stimulates uterine contractions and milk ejection during suckling

Question 17

Antidiuretic Hormone (ADH, also known as vasopressin)

Answer 17

Enhances water reabsorption by collecting duct cells of nephrons in the kidney

Question 18

Thyroid Gland

Answer 18

• Butterfly shaped gland on anterior surface of the superior part of the trachea (inferior to larynx)
• Thyroid Histology:
  
  • Follicles
  • Parafollicular cells

Question 19

Follicles

Answer 19

• Walls of the follicles are composed of epithelial (follicular) cells that secrete the hormone thyroxine (T4)
• Thyoxine is converted to its active form (T3) in target cells

Question 20

Parafollicular cells

Answer 20

• Between follicles
• Secrete calcitonin
  
  • Increase Ca++ uptake into bone (bone formation) which lowers blood Ca++

Question 21

Parathyroid Glands

Answer 21

• 4 (usually) glands embedded in posterior thyroid
• Secrete parathyroid hormone (PTH)
  
  • Acts on bone, kidneys to increase blood calcium levels

Question 22

Adrenal Glands

Answer 22

• Located on the superior surface of each kidney
• Parts:
  
  1. Adrenal Cortex (outer)
  2. Adrenal Medulla (inner)

Question 23

Adrenal Cortex (outer)

Answer 23

• Epithelial tissue forming glands
• Secretes only steroids
• 3 Layers ( a single class of hormones is secreted by each layer):
  
  1. Zona Glommerulosa
  2. Zona Fasciculata
  3. Zona Reticularis

Question 24

Zona Glommerulosa

Answer 24

• Mainly secretes aldosterone
  
  • Acts on nephrons to regulate salt balance

Question 25

Zona Fasciculata

Answer 25

- Secretes mainly cortisol - Regulates many body processes during long-term stress

Question 26

Zona Reticularis

Answer 26

- Secretes androgens (sex hormones) - Converted to testosterone or estrogens in other tissues

Question 27

Adrenal Medulla (inner)

Answer 27

- Modified nervous tissue - Synthesizes hormones that regulate "fight or flight" response - Epinephrine (80%) - Norepinephrine (20%)

Question 28

Endocrine Tissues

Answer 28

- Hormone secreting cells or tissues located in organs that have other functions (i.e. are not stricly glands that secrete hormones): 1. Pacreatic Islets of langerhans in Pancreaas 2. Hypothalamus (part of the brain) 3. Gonads 4. Others

Question 29

Hypothalamus (part of the brain)

Answer 29

- Produces and secretes hormones that stimulate or inhibit the secretion of hormones from the anterior pituitary - GHRH (Growth Hormone Releasing Hormone) - GHIH (Growth Hormone Inhibiting Hormone; also known as somatostatin) - GnRH (Gonadotropin Rleasing Hormone) - for FSH and LH secretion - Produces hormones that are stored and secreted by posterior pituitary

Question 29

Pacreatic Islets of langerhans in Pancreaas

Answer 29

- 𝛼-cells - Secrete glucagon - Increases blood glucose concentration - β-cells - Secrete insulin - Decreases blood glucose concentration

Question 30

Gonads

Answer 30

- Testes - Interstitial endocrine (Leydig) cells - secrete testosterone - Ovaries - Granulosa cells of secondary and vesicular follicles secrete estrogen - Corpus luteum secretes estrogen and progesterone

Question 31

Others

Answer 31

- Duodenum - secretin; cholecystokinin (CCK) - Kidney - renin, erythropoietin (EPO) - Skin - vitamin D - Heart - atrial natriuretic peptide (ANP) - and others